The present invention relates in general to fluid coupling apparatus for load and/or torque control and for use in a torque load simulator system.
As noted in U.S. Pat. No. 5,054,593 various types of electroactive fluids have been developed which consist of suspensions of very fine particles in a dielectric liquid media. Electroactive fluids experience changes in their properties in the presence of an electric field and have been used in various mechanical applications. One type of electroactive fluid is an electrorheological or "electroviscous" fluid. Electrorheological fluids are electroactive fluids which in the presence of an electric field of a high magnitude can exhibit a shear stress characteristic which increases with increasing electric field strength. Such electrorheological fluids have been utilized for variable clutch or brake assemblies. The electrorheological fluid devices, however, require the application of substantially high voltages in order to obtain the electric field of desired strength.
The '593 patent makes reference to another type of electroactive fluid which is an electrophoretic or "electroseparable" fluid. Electrophoretic fluids are suspensions similar to electrorheological fluids but are characterized by a different response to an applied electric field. The particles within electrophoretic fluids exhibit an electrophoretic migration. Generally, the electrophoretic action may be accomplished and maintained at much lower electric fields, since electrophoresis is a linear phenomenon with respect to electric field strength. However, the strength of an electrotheological fluid varies with the square of the electric field.
Because electrophoretic fluids operate in a substantially different manner from electrorheological fluids in the presence of an electric field, their use in existing electrorheological fluid clutches and other devices may not be functional. In addition a viscous drag is provided by the fluid in suspension when no power is applied. At the same time the coupling forces which may be achieved can be relatively low.
In the present invention it has been found advantageous to utilize a magnetorheological fluid for selectively coupling related members. Patents relating to magnetorheological fluids include U.S. Pat. No. 2,996,162 issued Aug. 15, 1961 to Lehde, U.S. Pat. No. 3,250,341 issued May 10, 1966 to Takahashi, U.S. Pat. No. 3,439,787 issued Apr. 22, 1969 to Minciotti et al and U.S. Pat. No. 4,664,236 issued May 12, 1987 to Stangroom.
With use of a magnetorheological fluid, a magnetic field is utilized which can be controlled by a electromagnetically generated magnetic field. The magnetic field can be generated with a relatively low voltage in response to which the yield strength in shear of the fluid will vary, i.e. increase with increases in the intensity of the magnetic field. At the same time in order to provide a high yield strength in shear the magnetorheological fluid utilized may exhibit a relatively high viscous drag characteristic in the non-energized state, i.e. when the magnetic field is removed. In this regard, however, the unique design of the present invention provides a structure in which the viscous drag during non-energization is minimized while the response to the application and variation in intensity of the magnetic field is optimized.
It is therefore an object of the present invention to provide a unique and improved fluid coupling apparatus which utilizes a magnetorheological fluid.
It is another object of the present invention to provide a fluid coupling apparatus having a unique design including a rotating member having a structure with a minimum moment of inertia whereby the response of the apparatus to variations in the strength of the magnetic field will be optimized.
It is still another object of the present invention to utilize a magnetorheological fluid having a predetermined high level of yield in shear when energized and at the same time to provide a coupling design in which the effects of viscous drag from the fluid, when not energized, will be minimized.
In the application of these and other objects, a torque transmission and conversion apparatus is provided utilizing a magnetorheological fluid which is controlled by the application of a magnetic field. The apparatus may be configured as a clutch, brake, differential or other torque coupling assembly and includes cooperating members which can be connected as drive and driven or reaction elements. The magnetorheological fluid operates in surface contact with the members for providing selective coupling therebetween.
In one form of the invention, the fluid coupling device is advantageously utilized in a torque load simulator system whereby the resistance to applied torque by a torque tool can be varied by varying the intensity of the magnetic field on the magnetorheological fluid to simulate the load encountered in driving a fastener in a particular application. With such a system the functioning of torque tools can be periodically monitored for performance and maintenance purposes. In addition the joint simulator system can be utilized for endurance testing of a torque tool to determine its suitability for a particular application and/or to assist in the general design and evaluation of a torque tool.
As will be seen, the joint simulator system of the present invention provides considerable advantages over existing simulator systems which are generally mechanically controlled. For example, with existing mechanical systems the torque on a joint is simulated by threading a member down against a preselected resistance; when this is completed the fastening mechanism must be released from the tool and the threaded structure reversed or unthreaded back to its original position. This can be a relatively time consuming process. In the present invention, the joint simulator can be quickly returned to its initial, no load condition by simply removing the excitation current generating the magnetic coupling field. This can be achieved without the necessity of removing the tool and is especially advantageous where an endurance test is being conducted requiring numerous repetitive load cycles.
Thus it is another object of the present invention to provide a unique fluid coupling device utilizing a magnetorheological fluid in a torque load simulator system whereby the performance of torque tools can be tested and/or evaluated under selectively variable load conditions.
Other objects, features and advantages of the present invention will become apparent from the subsequent description and the appended claims, taken in conjunction with the accompanying drawings, in which: